Electrical measuring instrument



July 1l, 1950 F. x. LAMB 2,515,014

ELECTRICAL MEASURING INSTRUMENT Filed May 8, 1946 Patented July 11, 1950 UNITED sTArEs PATraN'I OFFICE Francis X. Lamln-East Orange,.N. J assignor'to Weston Electrical Instrument Corporation, Newark, N. J., a corporation of New Jersey Application May 8, 1946, `Serial No. 668,172 A l This invention relates to electrical measuring instruments and more particularly to long scale measuring instruments which may be manufactured, when desired, in substantially smaller sizes than has been possible with the prior typeso long scale instruments.

The conventional instruments of the permanent magnet-pivoted coil type have a scale length of about 90, and the prior permanent magnet constructions for extending the scale to an angular length of the order of up to 200 to 270 have been relatively complex,'expensive and of large size. It is advantageous for various reasons to manufacture electrical measuring instruments in small or miniature sizes that may be housed in casings having an outside diameter of, for example, about 1.5 inches. The scale length for an instrument of conventional design and of such small size would be about 0.7 inch, and the scale graduations would be so crowded as to preclude an accurate reading of the measuredvalue. The design requirements for prior instruments of the long scale type are such that it is not possible to manufacture the known instruments in such claims. (61.171.495)

small size as to t within a casing having a diam- Y' eter of the order of 1.5 inches.

An object-of the present invention .is to provide miniature electrical measuring instruments having scales of long angular and linear extent. An object is to provide miniature instruments having a scale length in excess of the diameter of the instrument casing. More specifically, an object is to provide electrical measuring instruments of the pivoted coil type in which the length of the instrument scale is substantially greater than the outside diameter of the instrument casing. A further specific object is to provide a single air gap type of permanent magnet-pivoted coil instrument in which the magnetic neld system includes a cylindrical, radially charged permanent magnet having a circumferential length approximating the angular length of the instrument scale and a cylindrical soft iron yoke about the permanent magnet, the moving coil of the instrument being pivotally mounted for rotation about the axis of the magnet.

These and other objects and advantages of the invention will be apparent from the following specification when takenwith the accompanying drawing in which: f-

Fig. 1 is a somewhat schematic view oit-the permanent magnet yand moving coil systems of an electrical measuring instrument embodying the invention; the parts being shown vwithin their;-

2 strument casing and the moving coil being at ap'- proximately its mid-position;

Fig. 2 isa front elevation of the instrument, with parts broken away from the right side of the view to show the casing shell and the instrument proper in elevation;

Fig. 3 is a vertical section through the instrument on substantially the plane indicated by 1in 3--3 of Fig. 2; and

Fig. 4 is a fragmentary section on the plane indicated by line 4-4 of Fig. 2.

In the drawings, the reference numeral I identif-les a radially charged magnet of generally, annular form but of incomplete or C-shape with a circumferential length of somewhat more than the desired 4angular length of the instrument scale. An inner liux collector of soft iron is secured to and in magnetic contact with the inner surface of the magnet I; the ux collector being in two parts, oneof hook shape and comprising an incomplete annulus 2 iitted within the magnet l and terminating in a base section 3, and the other part being ailllet or wedge 4 that is secured to the base 3 by a screw 5 to iill the gap between the base 3 and the outer end of the hook 2. An outer'rng or cylinder 6 of soft iron surrounds and is spaced radially from the magnet' I to provide an air gap 1, andthe'ba'se v3 of the inner flux collector is' connected mechanically and'. magnetically to the outer ring `I to provide-a vlow reluctance path for the magnetic flux.

The moving system of the instrument comprises a coil 8 supported eccentrically of a staff 9 which carries a pointer I0 and a counterweight II lfor the coil, the axis of the staii' 9 coinciding orsubstantiallycoinciding with the axis of the magnet I. The coil lI3 is of the usual rectangular form and it-s'urroundsth'e magnet I and ring ofthe coil being within the air gap-f1 and the inner side being within the substantially Eux-free interior of thel ring section 2. It will be apparent that the ring section2 of the inner flux collector must have a circumferential length of less than 360 to permit assembly of the coil 8 about the magnet l. The wedge 4 is necessary tovobtain a uniformly graduated lor linear scale as it provides a uniformwlux density along the air gap 1, but the wedge 4 may be omitted when graduations are `to be 'compressed at one end of the scale. Theillustrated geometrical design of the xed and removable portions of the inner iiux collector is the presently; preferred construction 'but it, will' be apparent that other geometrical designs of these complementary parts may be employed.

The instrument is of the single air gap type as the torque is determined substantially exclusively by the outer side of the coil 8 and the ux distribution along the air gap l. Some leakage flux may be cut by the upper and lower ends of the coil 8 but, in general, this leakage ."luxzis fcifariegligible magnitude.

Annular plates I2, I2' are secured to the endsl I I f 'collector in magnetic contact with the inner surof the soft iron ring E, the plates being preferably" of soft iron to constitute shieldsyforitnefmagnetic 3 structure of the instrument. As the plates I2, I2' overlie the effective flux gapfjwithin which'fthe movable coil 8 rotates, it 'isapparent vthat "the deflection characteristics of the'ins'trument may7 be varied or controlled by propershapingio'th'e plates and their position with respect. to `.the magnet I and the soft-iron ring 6. Posts YI3 'are secured to and project "from the annulus I2 to support the scale plate 'I4 and a bridge vr'I5 in which a bearing I 6 torlthlestaig is mounted. The outer stafffbearing I'I is mounted astrap I8 which is integral with and extends diagonally across the annulu's I2".

The described instrument assemblyis mounted upon the insulating base fIllS oi lt'he'casing 2by -extensions i6' of the outerlsoft l-ironfririg andthe assembly is housed within the cylindrical casing shell `Whichiis also securedto the'ba'se I9. The illustrated instrument iisoff the-panel 'mounting type and 'the casing shell 'has an iouter `flange f2I of rectangular orm fto which an outer rcollar 22 of the same 'outline is secured lay-screws 123. projecting portions-of the colla-r 522 haveopenings 24 for receiving the studs yor bolts by 'which the instrument casing `lis mounted upon a panel. YA cover glass 25 is fitted `into the collar '22 and 1a zero ycorrection vvsystem 26 lis 'supported on the cover glass for adjustment fof 'thefouter end of Lone ofthe spiral springs S21 through 'which the coil 8 is 'connected' 'to terminals off e, rica-bie iconnector 29 which is @secured "to `the insulating base I9. Y

Instruments embodying the -invention -may be manufactured in any desiredrsize but the maximum advantages of the invention areobtainedin miniature instruments which 'have long 4.scales comparable to those off `substantially larger fin struments of conventional design. .As instrument according to this invention and o-ffxltfinches outside diameter with 12.22495 scaleof 1.9inch diameter maybe read'to the sameeccuracy -as -aconaY ventional instrument with :a 90 scale of about 2.75 inches diameter. lTh-e size of instruments embodying the invention-maybe reduced turther by employing the outer-ring -6 as the casing of the instrument. The illustrated instrument has a inner iiux collector being open at the circumferential gap of said magnet to permit assembly of said coil about said magnet, a magnetic material part for completing the full circumferential length of said inner flux collector after the assembly of the coil about the magnet, and means supporting said coil for rotational movement 'about substantially the eairisgof said irnja'grret.

2.-"An electricalinstrment comprising a radially charged C-shaped magnet, an inner flux y.tace.of'the:magnet-and having a radial extension projecting outwardly through the circumferential gap ol Vsaid :magnetfan outer flux collector ring means supporting said coil for rotational moveuniform scale characteristic as the y.inner face of l the rings land the outer face of the magnet I :are coaxial but other scale characteristics may be had by shaping the inner `surface of -thering to obtain an air gap 'I of varying .radial widthlor by an eccentric arrangement of the-opposedcylindrical surfaces forma-griet *I `alluring 6. y

I claim: A .1. An electrical instrument comprising .a .radil ally charged -C-shaped magnet-means ,providing a magnetic .material ,path v.for the .flux ofsaid magnet; said rmeansf'-i.nelud-ing .an yinner .iiux collector in magnetic contact with the .innersurface of the magnet and an :outer rlux collector ring spaced from the magnet bya ,radial gap, a coil having an 'inner side Within .said` inner cllector and an outer side Vin said radial gap, said ment-about substantially the axis of said magnet, said collector ring being. .in magnetic contact with the :1ra'dial-- extension of said inner 'fux collector.

3. f electricalzinstrument comprising :a tradially chargedr `magnet '.ofincompl'ete annulus form having a circumferentialigln means providinga mago etic material ,ipathffor :the `il-ux ci said mag: net, said means including :asoftiron .flux coblector ring .within said '.magnet, -a .'fsoft .iron :ring outsidefof and spaced :radially fromsaid magnet, a coil having an lir-iner-side `within f-said `iiux Ycollector ririg and :anjou-ter sidein-the -gap between said magnet .and said-outside ring, means supporting said coil ,for rotational movement, and a magnetic shield carried by -saidoutside ring.

.4. AAn electrical .instrumentcomprising a radially .charged Y.magnetof incomplete .annulus Aform having a circumferential gap, .a soft iron flux collectorring withinsaid magnet,..a soft iron ring outside .o-ffand spaced radiallyfrom said magnet, means cooperating with .said rings .to complete areturn path of llow reluctance for the magnetic flux, a coilfhaving an Ainner sidevwithin said ilux collector ring and an outer side in the .gap bet'vveenisaidA magnet. and said outside ring, means supportmg said coil for rotationalmovement, and acasin'g having abajse and .a shell, lsaido'uside ring extending axially Lbeyo'ndY said magnet and being supported on said base.'

55. A n velectrical"instrument comprising la radiallyjcharged magnet 'olf' incomplete rannulus form having a circumferential gap,"a soft iron 'flux 'collector'ring `within vsaid magnet, a softiron ring outside'o'fand space-d 'radially from Vsaid magnet, said outsidering extending axially beyond said magnet, means cooperating with 4said rings to complete a return patnof low reluctance `for the magnetic iiuX, va coil having an inner side within said flux collector ring andan outer 'side in the gap between said lmagnet and said outside ring, and meansfsuppor'tinglsaid 'coil 'for rotational movementgsaid coil-*supporting means including a fsoftiiron shield plate attached to said outside ring. l v

REFERENCES CITED The following references-are of record in the file of this patent:`r

Number Name Y i Date 996,377 Thompson et` al; June"27,'1,9`l'1 1,985,082 Faust; 1 Dec. 18, i934 T2,272,767 u Corson et al. Feb. 1-0, 1942 2,394,113 Seaver :et 'al,- ;Feb. 5, '11946 '2,422,714 Bigelow etal. "June"24, 1794*? 

